1. Field of the Invention
The present invention relates to a power clutch actuating system for vehicles having a change-speed transmission and a clutch in the drive train, and it relates more particularly to a system for sequencing clutch re-engagement in a plurality of discrete steps or stages.
2. Description of the Prior Art
There have been numerous attempts since the 1930's to provide a satisfactory system for servomotor actuation of the clutch of a manual transmission type vehicle, as evidenced by the large number of U.S. Letters Patent that have issued on systems of this general type. Most of these systems power the servo with an air pressure differential developed between atmospheric pressure and vacuum that is available in the intake manifold, or the carburetor throat below the throttle valve, of the engine of a gasoline powered vehicle.
Currently, due to very high and still increasing fuel costs, there is mass return to manual transmissions, generally in small automobiles, because of a considerably greater torque transmitting efficiency of manual transmissions than current state-of-the-art automatic transmissions. There has been a recent increase in the amount of U.S. patent art in this field, and this recent U.S. patent art indicates that at least one major Japanese automobile manufacturer which has large sales in the United States has for several years been expending a considerable amount of developmental effort seeking to achieve a satisfactory clutch actuating system.
The extensive relevant U.S. patent art discloses that the principal problem that those working in this art have had to overcome has been the difficulty of achieving smooth clutch re-engagement that is properly coordinated with torque demands on the vehicle drive train, this problem being most critical for clutch re-engagement when the vehicle is being accelerated from a standstill, at which time torque demands are generally at the highest and most variable levels. Numerous solutions have been proposed for solving this problem, most of them employing a plurality of steps or stages in the clutch re-engagement cycle, in which the clutch is allowed in a first step or stage to move from its fully disengaged position through a disengagement displacement range to a position near where first clutch contact is made; and then is allowed in one or more further steps or stages to move through a partial torque transfer range to its fully engaged position. However, prior to the present invention all such proposals for effecting clutch re-engagement in successive steps or stages have been undesirably complicated and critical not only as to performance but also as to installation and adjustment, requiring multiple solenoids, complex interrelated valves, valves that are at least partially controlled by vacuum sensed at some point in the carburetor throat, valves that are partially controlled by associated secondary servomotors, and the like.
Because of the difficulty and complexity of such prior art proposals seeking to obtain smooth, properly coordinated clutch re-engagement, particularly where the vehicle is starting up from a standstill, some of the prior art systems have simply included a torque converter or centrifugal clutch in the system to ease in the initial torque transfer through the drive train. An example of such a system that includes a torque converter is the Volkswagen "Automatic Stick Shift" system which it is believed came onto the market in the late 1960's, and appears to embody both the torque converter arrangement disclosed in the Binder U.S. Pat. No. 2,891,640 and the complex multiple interrelated valve system disclosed in the Von Bomhard U.S. Pat. No. 2,974,765. Examples of such systems that include centrifugal clutches are the Binder U.S. Pat. No. 2,766,862 and Von Bomhard U.S. Pat. No. 2,949,174. These centrifugal clutch systems are additionally complicated by mechanisms for advancing the throttle or richening the fuel mixture to keep the centrifugal clutch engaged when the servo clutch actuator is operated for shifting between gears while the vehicle is in motion. The addition of a torque converter or centrifugal clutch in connection with a servo clutch actuator mechanism makes the overall system undesirably expensive and has the limitation that it can only be employed as original equipment, and can not be retrofitted to the large market of already existing vehicles.
In the prior art clutch actuating systems which release the clutch back into engagement in a plurality of discrete steps or stages after the clutch has been disengaged by servo actuation, it has been the mechanisms for effecting the first stage of the clutch re-engagement cycle that have made the systems over-complicated and critical in adjustment and performance.
While the prior art discloses relatively simple means such as a small bleed orifice or a throttle-controlled bleed valve providing communication between the servo actuating chamber and atmospheric pressure for effecting the final stage of the clutch re-engagement cycle during which the clutch is allowed to move from the first stage position to the full clutch engagement position, such bleeding of atmospheric pressure to the servo chamber was nevertheless critical due to the small volume of the servo actuating chamber, and the correspondingly small amount of air involved in the bleeding process relative to the considerable amount of clutch movement sought to be controlled thereby.
The prior art systems for effecting the first step or stage of a multiple stage clutch re-engagement cycle fall into four distinct categories: (1) Multiple, cooperating valve mechanisms, including a solenoid valve which first closes off communication between a high vacuum (or in one case pressure) source and a servo which had been actuated thereby, and another valve, in some cases solenoid-actuated, then proceeds to establish a lower vacuum (or pressure) condition in the servo to effect the first stage of the clutch re-engagement cycle. (2) A double-acting sort of piston or diaphragm clutch actuator employing a complex arrangement of solenoids and valves in which release of vacuum from one side of the piston or diaphragm initiates the first stage of the clutch re-engagement cycle, and pressure buildup on the other side of the piston or diaphragm stops the latter at the first stage position. (3) Employment of a further vacuum servo motor device in addition to the clutch actuating servo, the additional servo cooperating with the primary servo or with a control valve to effect the first stage of the clutch re-engagement cycle. (4) A complex, critical rotary valve associated with the servo actuator solenoid valve provided with multiple porting to effect a two-stage clutch re-engagement cycle through linkage with the throttle.
In all four categories the first clutch re-engagement stage, just as the final stage, was made critical as to adjustment and performance due to the relatively small volume, only approximately that of the servo actuating chamber, being adjusted as to vacuum or pressure level in effecting the first re-engagement stage.
The following U.S. Letters Patent fall within the first category referred to above: Haubourdin et al, U.S. Pat. No. 2,763,347, in which a first solenoid valve shuts off a high vacuum source from the servo, and second solenoid is switched on by clutch movement to define the first stage of the re-engagement cycle; and Von Bomhard U.S. Pat. No. 2,974,765 which discloses the multiple valve mechanism employed in the aforesaid Volkswagen "Automatic Stick Shift" system. Here, after the main solenoid valve was de-energized to cut off communication from a high vacuum source to the clutch servo, a pressure regulator valve commenced operating to bleed atmospheric pressure to the servo to establish a lower vacuum condition in the servo. A separate diaphragm vacuum-actuated servo connected to the pressure regulator valve adjusted the low vacuum level at which the regulator valve stopped admitting atmospheric air in accordance with carburetor throat pressure conditions above the throttle butterfly valve. When this multiple valve mechanism of Von Bomhard U.S. Pat. No. 2,974,765 was employed in practice in the Volkswagen "Automatic Stick Shift" system, it also required the presence of a torque converter in the drive train.
Continuing with the aforesaid first category U.S. patents, Toyota et al U.S. Pat. No. 4,061,217 employs an "air-on" solenoid valve that is switched on by the clutch servo actuator rod so as to be open to apply a gulp of air to the servo when the main solenoid valve cuts off the vacuum source from the servo; then, when the servo actuator rod has moved part way through its stroke, it opens the "air-on" solenoid switch to shut off the atmospheric air and define the first re-engagement stage. Matsumoto et al U.S. Pat. No. 4,248,333 employs the same system as Toyota et al U.S. Pat. No. 4,061,217, in a different structural arrangement. Toyota et al U.S. Pat. No. 4,234,066 employs what is basically the same system of Toyota et al U.S. Pat. No. 4,061,217 and Matsumoto et al U.S. Pat. No. 4,248,333, except that the separate "air-on" solenoid valve is de-energized to define the first stage of the re-engagement cycle by decay in an electrical timing circuit. Michell et al U.S. Pat. No. 3,074,524 discloses an air pressure clutch servo system in which clutch re-engagement is initiated by de-energization of a clutch actuator solenoid valve, and a separate "clutch apply" valve controls the rate of release of air pressure according to engine RPM as indicated by engine water pump output.
The complexity appears to have arisen in this first category of prior art clutch re-engagement patents because they all require some secondary valve means that must be initiated into operation in sequence to establish the low vacuum condition for the first stage of the re-engagement cycle after the primary solenoid valve has been released to cut off the high vacuum source from the servo.
Referring now to the second category of systems for effecting the first stage of clutch re-engagement, in which pressure buildup on the back side of the servo actuator piston or diaphragm stops the clutch at the first stage position, Thomas U.S. Pat. No. 2,531,711 requires two solenoid valves and a clutch actuator stem valve; Hruska U.S. Pat. No. 2,296,282 requires a complex multiple valve arrangement including a solenoid valve, multiple chambers connected by bleed ports at the back side of the servo diaphragm, a check valve to admit air into such chambers, a first stage pressure regulator valve which functions after the solenoid valve is released to establish the first stage servo diaphragm opposition pressure; and this system also requires a fluid clutch in addition to the friction clutch. The second category of patents also includes Price et al U.S. Pat. No. 2,057,740 which employs a solenoid valve, a check valve to admit air into a chamber at the back side of a double-ended clutch servomotor, and an actuator stem slide valve which starts pressure accumulating on the back side of the servo for the first stage positioning; and Fujimoto et al U.S. Pat. No. 3,303,912 which requires a solenoid valve, a complex slide valve associated with a pressure chamber at the back side of the actuator diaphragm, and a separate servo controlled by carburetor throat vacuum to adjust the slide valve.
The third category of patents referred to above which require an additional servomotor device to control, the first stage of clutch re-engagement includes Price U.S. Pat. No. 2,511,373, Von Bomhard U.S. Pat. No. 2,974,765 also referred to under category one above, Prather U.S. Pat. No. 2,665,785, Flinn U.S. Pat. No. 2,620,667, and Fujimoto et al. U.S. Pat. No. 3,303,912 referred to also under category two above.
The fourth category of patents referred to above includes Grassmuck U.S. Pat. No. 3,698,525, which includes in addition to a solenoid valve a related rotary valve with multiple porting, the rotary valve being critically mechanically linked to the throttle in an attempt to accomplish stepped or staged clutch re-engagement entirely through the throttle connection.
Another problem in this art is the provision of a durable, reliable, conveniently operable switch mechanism which when closed will energize the solenoid actuated valve to cause servo disengagement of the clutch, and which when again opened will initiate the first stage of the clutch re-engagement cycle. In most of the prior systems of this general type, the switch mechanism took one of three forms, (1) a switch in the gearshift knob actuated by push button on the top of the knob; (2) a switch associated with the gearshift lever proximate its root and arranged to close upon application of shifting force to the lever; and (3) a switch associated with the throttle and arranged to close upon closing of the throttle. Of these three forms, the throttle-controlled switch is presently preferred because it is the most reliable way to render the system fully automatic insofar as the clutch actuation part of gear shifting is concerned, and it also results in a considerable saving of fuel because of resulting free wheeling when there is no torque demand on the drive train. A simple system disconnect switch conveniently mounted, as on the vehicle dashboard, can then enable engine compression to be used for deceleration whenever desired.
Two recent U.S. Letters Patent disclose gearshift lever knob tilt switches in which the knob is pivotally mounted at its root on the upper end of the gearshift lever, and has its largest diameter, most bulbous portion at the upper end so that application of shifting force to the upper part of the knob will tilt the knob and close the switch, and release of such force will allow spring biasing means in the knob to reopen the switch. These two recent patents are Takeda et al U.S. Pat. No. 4,144,424 and Rumyantsev et al U.S. Pat. No. 4,183,424. Except for the throttle-controlled switch, the tiltable knob type switch is believed to be the most conveniently operable type of switch for clutch actuating systems of the general type referred to herein. However, the specific knob switches disclosed in the Takeda et al and Rumyantsev et al patents present problems. Each of them requires a special type of gearshift lever for mounting of the switch or conducting a hot lead therethrough, which precludes retrofitting of these two knob switches on the large market of existing automobiles. The pivotal mounting in the Takeda et al device precludes universal tilting and requires a non-rotatable gearshift lever; while the Rumyantsev et al tilting is not about a pivot structure, but is simply against a shoulder at the opposite side of the lever from the side to which the shifting force is applied, so pivoting is not as efficient as it would be with an axially centered pivot. Metal springs for centering the knobs and opening the switches in these two patents do not exert their primary force in the lateral direction required to center the knobs and open the switches; to the contrary, the springs in each of these patents exert their primary biasing force in an axial direction 90% offset from the required biasing result, and consequently are inefficent in their biasing action. Additionally, the devices of each of these two patents are undesirably complicated.
Another type of gearshift lever knob tilt switch is disclosed in Barth U.S. Pat. No. 3,061,058, in which the gearshift knob is split into upper and lower halves which bear the respective contacts, and the lower half is pivotal so that by placing the hand over the upper half and engaging fingers into the lower half, the lower half can be rocked up into the contacting position. This requires an unnatural grasping of the knob.